EP0026938B1 - Control of activated sludge wastewater treating process for enhanced phosphorus removal - Google Patents
Control of activated sludge wastewater treating process for enhanced phosphorus removal Download PDFInfo
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- EP0026938B1 EP0026938B1 EP19800106093 EP80106093A EP0026938B1 EP 0026938 B1 EP0026938 B1 EP 0026938B1 EP 19800106093 EP19800106093 EP 19800106093 EP 80106093 A EP80106093 A EP 80106093A EP 0026938 B1 EP0026938 B1 EP 0026938B1
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- mixed liquor
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/02—Aerobic processes
- C02F3/12—Activated sludge processes
- C02F3/1205—Particular type of activated sludge processes
- C02F3/1215—Combinations of activated sludge treatment with precipitation, flocculation, coagulation and separation of phosphates
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/006—Water distributors either inside a treatment tank or directing the water to several treatment tanks; Water treatment plants incorporating these distributors, with or without chemical or biological tanks
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/30—Aerobic and anaerobic processes
- C02F3/308—Biological phosphorus removal
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/10—Biological treatment of water, waste water, or sewage
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S210/00—Liquid purification or separation
- Y10S210/902—Materials removed
- Y10S210/903—Nitrogenous
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S210/00—Liquid purification or separation
- Y10S210/902—Materials removed
- Y10S210/906—Phosphorus containing
Definitions
- This invention relates to an improvement in a particular type of activated biomass process wherein the operating conditions of the system are controlled so as to maintain or to exceed a minimal phosphate removal rate, thus enhancing phosphorus removal from influent and simultaneously enhancing phosphorus uptake by biomass.
- the particular type of biomass process to which the present invention is applicable is one wherein a phosphate- and BOD-containing influent is mixed with recycled activated biomass in the initial contact step of the process, thereby producing a mixed liquor.
- This initial treating must be under anaerobic conditions, i.e., substantially free of oxygen and oxidizing agents and having a dissolved oxygen concentration of less than about 0.7 ppm.
- the biomass process further requires the subsequent treatment of the mixed liquor under oxic conditions thereby oxidizing BOD (Biological Oxygen Demand) in the mixed liquor and also causing storage of phosphates in the microorganisms.
- BOD Bio Oxygen Demand
- the mixed liquor is subjected to settling or separation whereby a purified supernatant liquid is separated from biomass, at least a portion of which settled biomass is returned to the initial contacting to provide the activated biomass admixed with the influent.
- the improvement of the present process is obtained by maintaining operating conditions in a biomass process of the type just described so as to enhance removal of phosphorus from the influent and incorporation thereof in the biomass in a high rate system.
- This patent also describes another variation of the basic type process wherein the mixed liquor is passed from the anaerobic zone to an anoxic zone (i.e. containing NO x, but substantially no dissolved oxygen) positioned intermediate the anaerobic and oxic zones.
- anoxic zone i.e. containing NO x, but substantially no dissolved oxygen
- Such process is effective to remove phosphorus from the influent and to cause the incorporation or storage of the phosphorus in the biomass.
- This initial contacting of influent and activated biomass effects the selective production of nonfilamentous microorganisms capable of sorbing BOD both under anaerobic conditions and under oxidizing conditions and capable of storing phosphorous-containing materials, hereinafter referred to as phosphates, under oxidizing conditions.
- the mixed liquor is treated in an oxic or oxygenating step by contacting with oxygen-containing gas so as to maintain a dissolved oxygen (DO) content of at least about one part per million (1 ppm).
- DO dissolved oxygen
- this mixed liquor which has been previously subjected to anaerobic treatment and then to oxic treatment, is subjected to separation, such as by wetting, whereby supernatant liquid is separated from biomass, and at least a portion of the separated biomass is returned to an initial contacting step to provide the activated biomass admixed with the influent.
- the improvement of the present invention comprises maintaining within the process system a particular set of inter-related operating conditions within a specific envelope described herein.
- the process system includes the portion of the processing scheme encompassing the initial anaerobic contacting and extending through all of the processing steps and/or zones of the process up to, but not including, the settling zone or step.
- the process system also encompasses any internal recycle streams such as, for example, the internal recycle of mixed liquor from an oxic zone to an anoxic zone of the Spector process described above as well as the sludge recycle stream from the separation or settling operation.
- the particular conditions which must be maintained within the process system include a ratio of influent soluble BOD s , exclusive of BOD due to ammonia, (expressed as milligrams of soluble BOD per liter of influent) to influent soluble phosphate expressed as phosphorous (P) in the aqueous phase (expressed as milligrams of phosphorus per liter of influent) in a ratio (BOD/P) of from 5:1 up to 50:1. Additionally, it is necessary to maintain a food to biomass (F/M) ratio from a minimum of 0.09 up to a maximum of 1.4. In the above ratio, F is the total mass of soluble BOD .
- the present invention is based upon the fact that when operating an activated biomass system of the particular type defined, the rate of phosphorus removal can be increased, and thus the overall phosphorus removal enhanced, by decreasing the detention time.
- the art has generally taken the position that if treatment of a phosphorus containing influent was effective to remove some of the phosphorus, then the way in which to remove more of the phosphorus was to increase the length of exposure of material being treated to biomass doing the treatment.
- the rate of phosphorus removal is increased by decreasing the exposure time of phosphorus containing influent to the particular biomass developed in the system. Through this increased rate of phosphorus removal, it thus becomes possible to enhance the total phosphorus removal.
- the means employed herein to define this enhanced area of operation is to select and operate within the proper ratios of F/M and BOD/P.
- F/M ratio it will be understood that, at a given concentration of VSS, the longer the detention time of the system, the greater will be the total biomass or total volatile suspended solids. Thus, for a given concentration of BOD in the influent and at a given influent flow rate, the effect of a longer detention time will be to lower the F/M ratio.
- the present process requires the employment of a minimum F/M ratio of 0.09; thus, in effect, providing a given system with a limited maximum detention time. Usually, however, the minimum F/M ratio will be at least 0.10 or even 0.11.
- the F/M, ratio selected will be at least 0.12 and more preferably at least 0.13.
- the upper limit of the F/M ratio to be employed in this process is to be maintained at least than 1.4 and generally will be less than 1.0.
- the F/M ratio is maintained at less than 0.75 or even 0.60.
- the F/M ratio to be employed in a particular system is related to the ratio of soluble BOD s to the soluble phosphate, expressed as elemental phosphorus (P) in the influent wastewater i.e.
- the maximum F/M to be employed is 0.6 and preferably is 0.3, when the BOD/P ratio is in the range from 5 to 10; when the BOD/P ratio is in the range from 10 to 20, then the maximum F/M ratio can be 1.0 and preferably is 0.45; and when the BOD/P ratio is in the range from 20 to 50, then the maximum F/M ratio to be employed is 1.4 and preferably 0.5.
- the maximum F/M ratio to be employed is 0.6 and preferably is 0.3, when the BOD/P ratio is in the range from 5 to 10; when the BOD/P ratio is in the range from 10 to 20, then the maximum F/M ratio can be 1.0 and preferably is 0.45; and when the BOD/P ratio is in the range from 20 to 50, then the maximum F/M ratio to be employed is 1.4 and preferably 0.5.
- enhanced P removal it is less advantageous to employ an F/M ratio greater than 1.0 regardless of BOD/P.
- the BOD/P ratio is to be at least 5:1, as mentioned above.
- the BOD/P ratio is at least 6:1 or even 8:1 with ratios of at least 10:1 being quite satisfactory.
- the improved process of our invention is advantageous when employed with BOD/P ratios of up to 50:1 and, although operable with higher ratios, the process is less advantageous.
- This is merely due to the practical consideration that in most influents, such as municipal sewage, this is the ratio at which phosphate is largely removed from conventional systems because "ordinary" biomass, i.e. containing from 1 to 2% phosphate, expressed as P, can remove most or all of the P, when the soluble BOD S /P ratio is greater than 50:1.
- the improved results achievable with the present process are more noticeable e BOD/P ratio is less than 50:1 and even more so at BOD/P ratios of less than 30:1 and even le 25:1.
- the improved results obtained in accordance with this invention are manifested in high rates of phosphorous removal.
- This high rate is characterized by a first ter reaction rate constant (k,) of at least about 0.5, which is maintained until the concentration of P n the aqueous portion of the mixed liquor is reduced to less than about 1 mg/I.
- k 1 values of greater than 0.75 and even greater than 1.0 can be achieved.
- the term k 1 is defined as milligrams of phosphorous removed per hour per milligram of phosphorous in the aqueous portion of the mixed liquor per gram of volatile suspended solids per liter in the oxic zone.
- P is soluble phosphate expressed as milligrams of phosphorous per liter
- t is nominal residence time in the oxic zone expressed in hours
- VSS is expressed in -rams per liter.
- the improved process of this invention is operable when employing an F/M ratio of at least 0.09, it is preferred to use an F/M ratio of a st 0.10 or even 0.11.
- the influent also contains ammonia values, ch are oxidized to nitrate and/or nitrite , in addition to BOD and phosphorus and at least a portio of the oxygenated mixed liquor is to be subjected to denitrification by BOD under anoxic conditions, it is preferred to employ slightly higher F/M ratios than would otherwise be employed. Accordingly, then, in such embodiment, it is preferred that the F/M ratio be at least 0.10 and preferably at least 0.11.
- F/M ratios of at least 0.12 and even 0.14 are particularly preferred when this mode of the basic process is employed.
- the reason for this higher minimal F/M ratio is to ensure that there is an adequate supply of BOD, to compensate for that utilized in denitrification. It is also preferred to use an F/M ratio no greater than 0.75.
- the F/M ratio employed will be less than 0.75 and preferably will be less than 0.6.
- the BOD content and the phosphorus content of the potential influent are not always that which might be desired by the operator and, accordingly, the introduction of a particular influent to a unit of fixed size, particularly an existing prior art unit, will not always, if ever, produce the BOD/P or F/M ratios and the interrelationship thereof as is required by the present process.
- Various techniques are available, however, in order to make the required adjustments.
- One is a substantial reduction in the overall size of the unit being employed.
- the number and size of the basins can be reduced drastically.
- traditional units designed for the biological removal of BOD have been sized so as to permit detention times on the order of from 15 to 20 hours up to several days.
- a unit constructed specifically to practice the improved process of this invention would be sized so as provide a detention time of less than about 10 hours, preferably less than about 7 hours with detention times of about 5 hours or less, such as 3y or even 2 hours, being quite feasible.
- a solution would be to bypass a substantial volume of the existing basin capacity.
- aeration can be eliminated in a portion of an oxic zone, thus, in effect, reducing the active volume under oxic treatment.
- the BOD/P ratio can be adjusted in several ways. If it is desired to increase the BOD/P ratio, this can be done by the addition of further BOD to the system. For example, by addition of extraneous BOD such as sugar, brewary waste or molasses.
- the BOD/P ratio in the system can be increased by removing phosphorus from the system by treatment with chemicals such as salts of aluminum (alum) or iron or physical chemical methods as described in EPA Manual "Process Design Manual for Phosphorous Removal", October 1971.
- chemicals such as salts of aluminum (alum) or iron or physical chemical methods as described in EPA Manual "Process Design Manual for Phosphorous Removal", October 1971.
- lime for phosphorus removal, while being operable, is not preferred.
- the BOD/P ratio can be reduced by the addition of sources of phosphorus such as phosphate rock which is at least partially solubilized within the system. While this may appear to run contrary to the general teachings of the art and the goals of the treating process, the present improved process is quite capable of efficiently removing both large quantities and high percentages of phosphorus from the influent so that the addition of phosphorus to the system is not only an acceptable procedure, but, in fact, may be desirable and advantageous inasmuch as it produces a relatively high phosphorus content sludge which can be of value in and of itself as explained more fully in the above- mentioned US ⁇ A ⁇ 4,162,153 of Spector.
- the F/M ratio in the system can also be adjusted through various techniques. Thus. if the F/M ratio is less than required in this improved process, it can be increased by the addition of BOD, such as sugar, to the process. It will be understood, that this also increases the BOD/P ratio. Another technique for increasing the F/M ratio is to take steps to decrease the value of M, for example by decreasing the sludge recycle rate. Still another technique for increasing the F/M ratio is merely to increase the influent flow rate. While with other processes the increase of the influent rate might generally be undesirable, such is not necessarily the case at the low F/M range of the present process since an increase in influent flow at a given BOD level results in higher F/M, lower detention time and icnreased rate of phosphorus removal.
- an acceptable technique is to increase the value of M or the value of the volatile suspended solids in the system by increasing the sludge recycle rate relative to influent rate, decreasing sludge purge from the system or a combination of both.
- the IDT of the anaerobic treatment it is desirable to control the IDT of the anaerobic treatment such that it represents at least 5% of the total IDT of the entire process system.
- the IDT of the anaerobic treatment represents at least 10% or even 20% of the total IDT of the process system.
- the IDT of the anaerobic treatment is usually controlled such that it constitutes no more than 80% of the total IDT of the process system.
- the IDT of the anaerobic treatment is no more than 70% or even 60% of the total IDT of the process system.
- the IDT of the oxic treatment for typical operations is controlled so that it comprises at least 20% of the total IDT of the process system. Controlling the oxic IDT so as to constitute at least 30% or even 40% of the total IDT of the process system is quite satisfactory. Normally, the IDT of the oxic treatment is controlled such that it represents less than 95% of the total IDT of the process system and, generally, is controlled so as to constitute less than 90% or even less than 80% of the total IDT of the process system.
- the IDT of the anoxic treatment is controlled so as to comprise at least 5% and usually at least 10% of the total IDT of the process system.
- the IDT of the anoxic treatment is controlled so that it comprises no more than 50% of the total IDT of the process system.
- the IDT of the anoxic treatment is controlled so that it constitutes less than 30% or even less than 20% of the total IDT of the process system.
- Another way of expressing the limits regarding the control of IDT's during the anaerobic and oxic treatments is to maintain control of the anaerobic and oxic treatment IDT's based upon the total IDT for only the anaerobic and oxic treatments, even if there are additional treatments in the process, such as, for example anoxic treatment.
- the IDT of the anaerobic treatment is to be at least 10% of the combined anaerobic and oxic IDT's while the IDT of the anaerobic zone should be controlled so as to be no greater than 70% or even 60% of the combined anaerobic and oxic IDT's.
- the IDT in the oxic treatment is to be controlled such that it comprises no more than 90% of the combined anaerobic and oxic lOTs.
- the IDT of the oxic treatment is to be controlled so as to comprise at least 30% or even 40% of the combined anaerobic and oxic lOTs.
- This invention also allows of the conduct of biological processes, such as, for example, fermentation, including the production of biosynthetic medicaments, in a controlled manner so as to obtain rapid incorporation of phosphorous into the active biomass.
- biological processes such as, for example, fermentation, including the production of biosynthetic medicaments
- the result of this is, of course, the maintenance of a biological population of high phosphorous content providing the advantages of ready separation of the more dense biomass from the liquor containing the product.
- the resulting high phosphorous content biomass contains its own internal source of energy, which permits the valuable biomass to survive anerobic conditions or to stand up to oxygen deficiencies in the system.
- an activated biomass system having an inlet line 10 for the introduction of a BOD- and phosphorus-containing influent.
- the influent can be wastewater from a primary sedimentation tank in a sewage treatment operation.
- the influent could be a BOD- and phosphorus-containing charge stock to a fermentation process.
- the influent initially enters an anaerobic mixing zone 12 wherein it is admixed with activated biomass introduced into mixing zone 12 by means of sludge recycle line 14 in order to form a mixed liquor.
- the anaerobic conditions defined above can be maintained, for example, by blanketing the liquid surface in zone 12 with nitrogen or other inert gas or by providing a cover to zone 12.
- Another means for insuring the maintenance of anaerobic conditions in zone 12 is to bubble nitrogen through the liquid in order to strip any oxygen therefrom. This particular technique is illustrated by means of manifold nitrogen inlet line 16 shown in Figure 1 as introducing nitrogen into the bottom of zone 12.
- the mixed liquor formed in anaerobic mixing zone 12 is then passed by means of line 18 into oxic treating zone 20 wherein the mixed liquor is contracted with an oxygen-containing gas.
- this is illustrated by means of spargers 22 designed to permit the contacting of mixed liquor with an oxygen-containing gas such as air, oxygen, or oxygen enriched air.
- the mixed liquor from oxic treating zone 20 is passed by means of line 24 into clarifier 26 wherein the mixed liquor is permitted to separate into a supernatant liquid phase and a more dense activated biomass phase.
- the supernatant liquid is removed from clarifier 26 by means of line 28 and then can be sterilized via ozone, chlorine or chlorine dioxide contacting and discharged to receiving waters, when the process is an activated sludge sewage treatment process.
- the liquid of line 28 can be recovered as the product-containing stream.
- the dense activated biomass layer 29 is maintained at a desired level by controlled removal from clarifier 26 by means of line 30. A portion of this activated biomass is removed from the system by line 32, while another portion of the activated biomass is recycled to the anaerobic mixing zone 12 by means of pump 33 and line 14.
- anaerobic mixing zone 12 can be a single treating stage, it is preferred to divide the anaerobic zone into a plurality of separate hydraulic stages. As illustrated in Figure 1, this can be accomplished through the use of partitions 34 which divide anaerobic zoning 12 into three interconnected stages. It will also be understood, of course, that zone 12 can be divided into a greater or lesser number of stages.
- zone 20 it is also preferred to have the oxic treating zone 20 divided into a plurality of interconnected hydraulic stages. This is illustrated in Figure 1 by means of the two partitions 36 which divide zone 20 into three stages. Again, it will be understood that zone 20 can also be divided into a greater or lesser number of stages.
- a process of the type illustrated by Figure 1 operates to effect incorporation of large quantities of phosphorus into the activate biomass, while causing the elimination of BOD from the liquid portion of the material treated; thereby providing a liquid effluent in line 28 of substantially reduced BOD and P content while providing an activated biomass, such as that removed from the clarifier by means of line 30, having a relatively high phosphorus content.
- the process system shown in Figure 1 to which the parameters of this invention relate is that portion of the flow scheme of Figure 1 enclosed within the dashed lines.
- This system has an inlet line 40 for the introduction of a BOD-, phosphorus-, and ammonia-containing influent.
- the influent is most typically a municipal or industrial wastewater stream. Alternatively, the influent can be the charge stock to a biosynthetic process, e.g. fermentation.
- the influent of line 40 initially enters an anaerobic mixing zone 42 wherein it is admixed with activated biomass introduced into mixing zone 42 by means of sludge recycle pump 69 and line 44 in order to form a mixed liquor.
- the mixed liquor formed in anaerobic mixing zone 42 is then passed by means of line 46 into anoxic treating zone 48 wherein the mixed liquor, containing BOD, is treated in the substantial absence of dissolved oxygen in order to convert nitrites and/or nitrates (NOX) into gaseous form, primarily N 2 , which is then removed from the system by bubbling off.
- NOX nitrites and/or nitrates
- the mixed liquor therefrom isd passed by means of line 52 into oxic treating zone 54.
- the mixed liquor introduced into oxic treating zone 54 still contains P, BOD, ammonia and ammoniacal compounds, which latte two materials pass through anaerobic mixing zone 42 and anoxic treating zone 48 substantially unaffected.
- this mixed liquor is contacted with an oxygen-containing gas.
- this is illustrated by means of spargers 56 designed to permit the contacting of mixed liquor with an oxygen-containing gas such as air, oxygen, or oxygen enriched air.
- this treating of the mixed liquor with oxygen is effective to convert ammonia and ammoniacal compounds into nitrites and/or nitrates.
- a portion of the mixed liquor containing these nitrites and nitrates is internally recycled from oxic treating zone 54 to anoxic treating zone 48 by means of pump 57 and internal recycle line 58.
- the material internally recycled by means of pump 57 and line 58 is the source of NO X subjected to the anoxic treatment in zone 48 as described previously.
- the mixed liquor therefrom is passed by means of line 60 into clarifier 62 wherein the mixed liquor is permitted to separate into a supernatant liquid phase and a more dense layer 65 of activated biomass.
- the supernatant liquid is removed from clarifier 62 by means of hne 64.
- This liquid can, if required, be sterilized and discharged to a stream or river in the form of purified water, when the process is an activated sludge sewage treatment process.
- the more dense layer 65 of activated biomass is maintained at a desired level by controlled removal from clarifier 62 by means of line 66. A portion of this activated biomass is removed from the system by line 68, while another portion of the activated biomass is recycled to the anaerobic mixing zone 42 by means of sludge recycle pump 69 and line 44.
- anaerobic mixing zone 42, the anoxic treating zone 48 and the oxic treating zone 54 can each be a single treating stage, it is preferred to divide each of these stages into a plurality of interconnected hydraulic stages. As illustrated in Figure 2 this can be accomplished through the use of partitions and two each of partitions 70, 72 and 74 are shown dividing anaerobic mixing zone 42, anoxic treating zone 48 and oxic treating zone 54, respectively, each into three separate stages. It will be understood, of course, that each of the zones can be divided into a greater or lesser number of individual stages and that it is not necessary for each of the zones to be divided into the same number of stages.
- FIG. 3 there can be seen a diagram of an activated biomass system having nitrification-dinitrification capabilities and having a flow scheme which is an alternative to that illustrated in Figure 2.
- This system has an inlet line 80 for the introduction of a BOD-, phosphorous-, and ammonia-containing influent into an anaerobic mixing zone 82 wherein it is admixed with activated biomass introduced into mixing zone 82 by means of sludge recycle line 84 in order to form a mixed liquor.
- the mixed liquor formed in anaerobic mixing zone 82 is then passed by means of line 86 into oxic treating zone 88.
- the mixed liquor introduced into zone 88 still contains BOD as well as P, ammonia and ammoniacal compounds, which latter two materials pass through anaerobic mixing zone 82 substantially unaffected.
- this mixed liquor is contacted with an oxygen-containing gas.
- this is illustrated by means of spargers 90 designed to permit the contacting of mixed liquor with an oxygen-containing gas such as air, oxygen or oxygen- enriched air in order to effect P and BOD removal.
- NOX nitrites and/or nitrates
- the technique illustrated in this figure is the employment of a manifolded nitrogen inlet line 96 designed to introduce nitrogen into the bottoms of zones 82 and 94. As discussed previously, this technique of bubbling nitrogen through the mixed liquor is effective to strip oxygen therefrom.
- the anoxic treatment of the mixed liquor is effective to convert the NO-x compounds into gaseous form, primarily N 2 , which can then be removed from the system by bubbling off.
- an additional and optional oxic treatment zone 110 having a sparger 108.
- This optional oxic treatment zone 110 is shown as being located between anoxic treating zone 94 and clarifier 100.
- This optional treating zone can be employed if it is desired to increase the dissolved oxygen content of the mixed liquor before introducing it into the clarifier 100.
- figure 4 there is shown a schematic plan view representing a hypothetical installed wastewater treating plant composed of two trains which are mirror images of each other.
- a wastewater influent line 112 which is split into lines 114 and 116, each of which provides wastewater influent to the first treating zones 118 and 120, respectively, of the parallel trains.
- sludge inlet lines 122 and 124 which introduce activated sludge into treating zones 118 and 120, respectively.
- Treating zones 118 and 120 are maintained under anaerobic conditions and it is in these zones that the initial contacting between influent and sludge is effected in order to produce mixed liquor.
- zones 118 and 120 Subsequent to the anaerobic treatment in zones 118 and 120 the anaerobically treated mixed liquor is then passed to anoxic treatment zones 128 and 130, respectively. This is represented by the arrows indicating flow from zones 118 and 120 into zones 128 and 130, respectively. (Flow from zone to zone elsewhere in this Figure is also represented by arrows.) In zones 128 and 130 the mixed liquor is subjected to anoxic treatment whereby denitrification is effected and NO is converted to nitrogen gas, which is then vented from the system.
- oxygen inlet manifolds 136 and 138 are illustrated as a means for introducing oxygen-containing gas into oxic treating zones 132 and 134, respectively.
- BOD is oxydized
- phosphate in the liquid portion of the mixed liquor are taken up by the biomass and ammonical nitrogen compounds are nitrified to form nitrites and nitrtes (NOX).
- mixed liquor internal recycle lines 140 and 142 which operate to transport NO, containing mixed liquor from oxic treating zones 132 and 134, respectively, to anoxic treating zones 128 and 130, respectively.
- NOX compounds in the mixed liquor are converted to elemental nitrogen gas in the anoxic treating zones.
- the mixed liquor from oxic treating zones 132 and 134 is then passed to the second anoxic treating zones 144 and 146, respectively.
- the treatment in these second anoxic zones is effective to further convert NO to elemental nitrogen gas which is then removed from the system.
- the mixed liquor from second anoxic zones 144 and 146 is passed to second oxic zones 148 and 150, respectively, wherein the mixed liquor is subjected to a second oxic treatment.
- Oxygen inlet lines 152 and 154 are illustrated as introducing oxygen-containing gas to second oxic treating zones 148 and 150, respectively.
- One of the purposes of this final oxic treatment is to raise the DO level of the mixed liquor to a high level before it is passed from oxic treating zones 148 and 150 by means of lines 156 and 158, respectively, to clarifier 160. This high DO level tends to keep the separated sludge from going anaerobic which would permit phosphorus bleed-out from the biomass.
- Clarifier 160 operates by permitting the separation of the mixed liquor into a more dense active biomass phase and a supernatent liquid phase, which liquid phase is removed from clarifier 160 by means of line 162.
- the more dense activated biomass is removed from clarifier 160 by means of line 164.
- a portion of the separated biomass is removed from the system by means of line 166, while another portion of the activated biomass is recycled to the initial anaerobic treating zone by means of line 168 which in turn connects with lines 122 and 124, described previously.
- a not untypical wastewater treating plant of the type described above and illustrated in figure 4 would have an IDT for all of the treating zones in the range of about 16 to 20 hours. Further the distribution of such total IDT, on a percentage basis, for the various treating zones illustrated would be about as follows:
- valves 170 and 172 are simply to install valves 170 and 172 in lines 114 and 122, respectively. To effect the change all that need be done is to reduce the rate at which activated sludge is being recycled via line 168 to a level of 50% of its former value while simultaneously closing valves 170 and 172.
- the methodology for determining the first order rate constant, k, is illustrated by using data relating to the operation designated as Example 6.
- the average profile of phosphate concentration in the oxic treating zone over a period of two weeks is shown below.
- VSS concentration for the period was 2.6 g/I.
- rate constant, k was calculated as follows:
- Example 1 illustrates operation employing a BOD/P ratio outside the scope of this invention, i.e. less than about 5, even though the F/M ratio was well into the acceptable range. Although this particular operation did result in substantial reduction in the BOD content and phosphorous content of the influent, the value of k 1 was less than 0.5.
- Example 2 through 11 the BOD/P ratio maintained was in the low range from about 5:1 up to about 10:1 and the F/M ratios varied within the defined limits.
- Examples 2 and 3 derived from different municipal wastewaters, illustrate that while the BOD/P ratios were within the limits required by the invention, the F/M ratios were just below the low end of the required envelope and the rate of removal of phosphorous was not consistently above the minimum level represented by a k,, value greater than 0.5.
- Examples 4 through 8 illustrate other experimental runs operating with similar BOD/P ratios but with increasing F/M ratios. Again, it is interesting to note that the highest value for k 1 of these five examples was achieved in Example 5, the one with the shortest detention time. (This excludes the results of anomalous Example 3.)
- Examples 9 through 11 illustrate an operation of the type illustrated in Figure 2 where the ammonia content of the influent was subjected to nitrification in an oxic zone and denitrification in an anoxic zone.
- the internal recycle rates for these three examples approached 200%.
- the F/M ratio was outside the range defined by the present invention and the k 1 value was substantially below the required 0.5 level.
- Examples 10 and 11 wherein BOD/P and F/M ratios within the defined ranges were employed, the values for k, were relatively high.
- Table II illustrates operations employing a BOD/P ratio in the range from about 10:1 up to about 20:1.
- Examples 12 and 13 employing different municipal wastewaters, illustrate that while the BOD/P ratios were within the limits required by the invention, the F/M ratios were just below the low end of the required envelope and the rate of removal of phosphorous was not consistently above the minimum level represented by a k 1 , value greater than 0.5.
- Examples 14 through 17 illustrate other experimental runs operating with similar BOD/P ratios but with increasing F/M ratios. Again, it will be seen that in many instances the result of decreasing detention time is to increase the value of the k i factor.
- Examples 18 through 20 exemplify an operation of the type illustrated in Figure 2 where the ammonia in the influent was subjected to nitrification in an oxic zone and denitrification in an anoxic zone.
- the internal recycle rates for these three examples varied from about 100 to about 200 per cent.
- Example 18 it will be seen that the value of the F/M ratio fell below the minimum acceptable level of 0.09 and that the value of k, also fell below the minimum standard of 0.5.
- the k, factor was substantially greater and above the minimum acceptable level.
Abstract
Description
- This invention relates to an improvement in a particular type of activated biomass process wherein the operating conditions of the system are controlled so as to maintain or to exceed a minimal phosphate removal rate, thus enhancing phosphorus removal from influent and simultaneously enhancing phosphorus uptake by biomass. The particular type of biomass process to which the present invention is applicable is one wherein a phosphate- and BOD-containing influent is mixed with recycled activated biomass in the initial contact step of the process, thereby producing a mixed liquor. This initial treating must be under anaerobic conditions, i.e., substantially free of oxygen and oxidizing agents and having a dissolved oxygen concentration of less than about 0.7 ppm. The biomass process further requires the subsequent treatment of the mixed liquor under oxic conditions thereby oxidizing BOD (Biological Oxygen Demand) in the mixed liquor and also causing storage of phosphates in the microorganisms. Subsequent to the oxic treatment, the mixed liquor is subjected to settling or separation whereby a purified supernatant liquid is separated from biomass, at least a portion of which settled biomass is returned to the initial contacting to provide the activated biomass admixed with the influent. The improvement of the present process is obtained by maintaining operating conditions in a biomass process of the type just described so as to enhance removal of phosphorus from the influent and incorporation thereof in the biomass in a high rate system.
- Illustrative of the activated biomass process to which the present invention is applicable are those described by Marshall L. Spector in US-A-4,056,456 entitled "Production of Non-bulking Activated Sludge", and in US-A-Patent 4,162,153 entitled "High Nitrogen and Phosphorous Content Biomass Produced by Treatment of a BOD-Containing Material." In the first patent there is described a process wherein the mixed liquor is initially formed in an anaerobic zone, and such mixed liquor is passed to an oxic zone where it is subjected to oxidizing treatment, and the oxidized mixed liquor is subsequently passed to a settling zone from whence a portion of the activated biomass is recycled to the initial anaerobic zone. This patent also describes another variation of the basic type process wherein the mixed liquor is passed from the anaerobic zone to an anoxic zone (i.e. containing NO x, but substantially no dissolved oxygen) positioned intermediate the anaerobic and oxic zones. In such variant there is also an internal recycle of mixed liquor from the oxic zone back to the anoxic zone, thus providing the NO in, the anoxic zone. It is also disclosed in this patent that such process is effective to remove phosphorus from the influent and to cause the incorporation or storage of the phosphorus in the biomass.
- This phenomenon wherein phosphorus is removed from influent and incorporated into biomass has been recognized by various people working in the area of wastewater treatment (see, for example, the references of record in the above mentioned patent).
- The difficulties with which the art has been confronted in the past have included the phenomenon that the removal of phosphorus from the influent in the traditional oxygenating systems has not always been consistent, i.e. sometimes it worked, and sometimes it did not work. In other wastewater treating processes where the primary thrust has been the removal of nitrogen compounds from the influent, again phosphorus removal was not consistent, and it was even believed that phosphorus removal was directly related to nitrogen removal. Additionally, in all of these prior art processes, the period of treating required has always been quite extensive ranging upwards of 15 to 20 hours or more. In the processes of the type to which the present invention relates, such as those described in the above-mentionned Spector patent, while phosphorus removal from the influent was always present, the extent or rate of phosphorus removal varied significantly, and there was no means provided for controlling such process to insure enhanced phosphorus removal, high rate processing and a basis for optimizing design of the system.
- It has now been found that enhanced phosphorus removal and operation of an adequately high rate process can be accomplished by maintaining a particular set of interrelated operating conditions within a specific envelope in a particular type of activated biomass process. The process to which the present improvement is applicable requires producing a mixed liquor by initially mixing recycled activated biomass with a phosphate- and BOD-containing influent under anaerobic conditions, i.e. substantially free of oxygen and oxidizing agents and containing a concentration of less than 0.7 ppm dissolved oxygen. This initial contacting of influent and activated biomass effects the selective production of nonfilamentous microorganisms capable of sorbing BOD both under anaerobic conditions and under oxidizing conditions and capable of storing phosphorous-containing materials, hereinafter referred to as phosphates, under oxidizing conditions. Subsequently, the mixed liquor is treated in an oxic or oxygenating step by contacting with oxygen-containing gas so as to maintain a dissolved oxygen (DO) content of at least about one part per million (1 ppm). Treatment under oxic conditions is effective to oxidize BOD in the mixed liquor and to cause storage of phosphates in the biomass. Finally, this mixed liquor which has been previously subjected to anaerobic treatment and then to oxic treatment, is subjected to separation, such as by wetting, whereby supernatant liquid is separated from biomass, and at least a portion of the separated biomass is returned to an initial contacting step to provide the activated biomass admixed with the influent.
- The improvement of the present invention comprises maintaining within the process system a particular set of inter-related operating conditions within a specific envelope described herein. The process system includes the portion of the processing scheme encompassing the initial anaerobic contacting and extending through all of the processing steps and/or zones of the process up to, but not including, the settling zone or step. The process system also encompasses any internal recycle streams such as, for example, the internal recycle of mixed liquor from an oxic zone to an anoxic zone of the Spector process described above as well as the sludge recycle stream from the separation or settling operation. The particular conditions which must be maintained within the process system include a ratio of influent soluble BODs, exclusive of BOD due to ammonia, (expressed as milligrams of soluble BOD per liter of influent) to influent soluble phosphate expressed as phosphorous (P) in the aqueous phase (expressed as milligrams of phosphorus per liter of influent) in a ratio (BOD/P) of from 5:1 up to 50:1. Additionally, it is necessary to maintain a food to biomass (F/M) ratio from a minimum of 0.09 up to a maximum of 1.4. In the above ratio, F is the total mass of soluble BOD., exclusive of ammoniacal BOD, introduced into the process system per 24-hour day, expressed as milligrams per day, while M is the total weight of volatile suspended solids (VSS) in the process system, expressed in milligrams. Normally, the F/M ratio will be no greater than 1.0.
- In one aspect, namely in the establishment of a minimum F/M value at one end of the envelope (the lower end), the discovery upon which this invention is based is somewhat surprising in that it appears to run contrary to the general consensus in the industry. Thus, for example, those wastewater treating processes wherein phosphorus removal has been noted are of a type which can be termed "low rate systems". When dealing with systems of this latter type, the consensus of the industry appeared to be that the means of accomplishing increased phosphorus removal is to increase the detention time in the system, thereby (the theory went) increasing the time in which the biological process had an opportunity to work. As opposed to this, the present invention is based upon the fact that when operating an activated biomass system of the particular type defined, the rate of phosphorus removal can be increased, and thus the overall phosphorus removal enhanced, by decreasing the detention time. To express this in another manner, the art has generally taken the position that if treatment of a phosphorus containing influent was effective to remove some of the phosphorus, then the way in which to remove more of the phosphorus was to increase the length of exposure of material being treated to biomass doing the treatment. Diametrically opposed to this is the present process wherein the rate of phosphorus removal is increased by decreasing the exposure time of phosphorus containing influent to the particular biomass developed in the system. Through this increased rate of phosphorus removal, it thus becomes possible to enhance the total phosphorus removal.
- The means employed herein to define this enhanced area of operation is to select and operate within the proper ratios of F/M and BOD/P. In defining the F/M ratio it will be understood that, at a given concentration of VSS, the longer the detention time of the system, the greater will be the total biomass or total volatile suspended solids. Thus, for a given concentration of BOD in the influent and at a given influent flow rate, the effect of a longer detention time will be to lower the F/M ratio. The present process requires the employment of a minimum F/M ratio of 0.09; thus, in effect, providing a given system with a limited maximum detention time. Usually, however, the minimum F/M ratio will be at least 0.10 or even 0.11. Preferably the F/M, ratio selected will be at least 0.12 and more preferably at least 0.13.
- On the other hand, however, this phenomenon which has been discovered does not continue indefinitely, but rather there are upper limits of the F/M ratio or lower limits to the detention time to be employed at the other end (the higher end) of the envelope for a given system. In this connection, it has been discovered that the upper limit of the F/M ratio to be employed in this process is to be maintained at least than 1.4 and generally will be less than 1.0. Preferably, the F/M ratio is maintained at less than 0.75 or even 0.60. Furthermore, it has been found that the F/M ratio to be employed in a particular system is related to the ratio of soluble BODs to the soluble phosphate, expressed as elemental phosphorus (P) in the influent wastewater i.e. the BOD/P ratio, Thus, with respect to enhanced rate of P removal, the maximum F/M to be employed is 0.6 and preferably is 0.3, when the BOD/P ratio is in the range from 5 to 10; when the BOD/P ratio is in the range from 10 to 20, then the maximum F/M ratio can be 1.0 and preferably is 0.45; and when the BOD/P ratio is in the range from 20 to 50, then the maximum F/M ratio to be employed is 1.4 and preferably 0.5. With respect to enhanced P removal it is less advantageous to employ an F/M ratio greater than 1.0 regardless of BOD/P.
- In the operation of the improved process of this invention, the BOD/P ratio is to be at least 5:1, as mentioned above. Preferably, the BOD/P ratio is at least 6:1 or even 8:1 with ratios of at least 10:1 being quite satisfactory.
- At the high end of the F/M spectrum the improved process of our invention is advantageous when employed with BOD/P ratios of up to 50:1 and, although operable with higher ratios, the process is less advantageous. This is merely due to the practical consideration that in most influents, such as municipal sewage, this is the ratio at which phosphate is largely removed from conventional systems because "ordinary" biomass, i.e. containing from 1 to 2% phosphate, expressed as P, can remove most or all of the P, when the soluble BODS/P ratio is greater than 50:1. The improved results achievable with the present process are more noticeable e BOD/P ratio is less than 50:1 and even more so at BOD/P ratios of less than 30:1 and even le 25:1.
- The improved results obtained in accordance with this invention are manifested in high rates of phosphorous removal. This high rate is characterized by a first ter reaction rate constant (k,) of at least about 0.5, which is maintained until the concentration of P n the aqueous portion of the mixed liquor is reduced to less than about 1 mg/I. With proper selection of operating parameters, k1 values of greater than 0.75 and even greater than 1.0 can be achieved. The term k1 is defined as milligrams of phosphorous removed per hour per milligram of phosphorous in the aqueous portion of the mixed liquor per gram of volatile suspended solids per liter in the oxic zone. Expressed in mathematical form then
- While, as mentioned above, the improved process of this invention is operable when employing an F/M ratio of at least 0.09, it is preferred to use an F/M ratio of a st 0.10 or even 0.11. It should also be noted that when the influent also contains ammonia values, ch are oxidized to nitrate and/or nitrite
- With respect to systems which must perform a nitrifying function it is also preferred that the F/M ratio employed will be less than 0.75 and preferably will be less than 0.6.
- As will be understood, the BOD content and the phosphorus content of the potential influent are not always that which might be desired by the operator and, accordingly, the introduction of a particular influent to a unit of fixed size, particularly an existing prior art unit, will not always, if ever, produce the BOD/P or F/M ratios and the interrelationship thereof as is required by the present process. Various techniques are available, however, in order to make the required adjustments. One is a substantial reduction in the overall size of the unit being employed. For units being constructed for the purpose of practicing this improved process, the number and size of the basins can be reduced drastically. Thus, for example, traditional units designed for the biological removal of BOD have been sized so as to permit detention times on the order of from 15 to 20 hours up to several days. As distinguished from this, a unit constructed specifically to practice the improved process of this invention would be sized so as provide a detention time of less than about 10 hours, preferably less than about 7
- Even with a newly constructed unit which has been designed specifically for the practice of this improved process, it may be necessary from time to time to make lesser adjustments in the operating conditions in the plant. This is particularly so in a wastewater treating plant when the BOD and phosphorus content, as well as the concentrations thereof, can vary noticeably from one time of day to another, as well as from one season of the year to another. These less than gross changes in operating conditions can be affected by lesser modifications and adjustments. Thus, for example, the BOD/P ratio can be adjusted in several ways. If it is desired to increase the BOD/P ratio, this can be done by the addition of further BOD to the system. For example, by addition of extraneous BOD such as sugar, brewary waste or molasses. Similarly, the BOD/P ratio in the system can be increased by removing phosphorus from the system by treatment with chemicals such as salts of aluminum (alum) or iron or physical chemical methods as described in EPA Manual "Process Design Manual for Phosphorous Removal", October 1971. In this connection, it should be noted that the use of lime for phosphorus removal, while being operable, is not preferred.
- Conversely, the BOD/P ratio can be reduced by the addition of sources of phosphorus such as phosphate rock which is at least partially solubilized within the system. While this may appear to run contrary to the general teachings of the art and the goals of the treating process, the present improved process is quite capable of efficiently removing both large quantities and high percentages of phosphorus from the influent so that the addition of phosphorus to the system is not only an acceptable procedure, but, in fact, may be desirable and advantageous inasmuch as it produces a relatively high phosphorus content sludge which can be of value in and of itself as explained more fully in the above- mentioned US―A―4,162,153 of Spector.
- The F/M ratio in the system can also be adjusted through various techniques. Thus. if the F/M ratio is less than required in this improved process, it can be increased by the addition of BOD, such as sugar, to the process. It will be understood, that this also increases the BOD/P ratio. Another technique for increasing the F/M ratio is to take steps to decrease the value of M, for example by decreasing the sludge recycle rate. Still another technique for increasing the F/M ratio is merely to increase the influent flow rate. While with other processes the increase of the influent rate might generally be undesirable, such is not necessarily the case at the low F/M range of the present process since an increase in influent flow at a given BOD level results in higher F/M, lower detention time and icnreased rate of phosphorus removal. On the other hand, however, if it is desired to decrease the F/M ratio, an acceptable technique is to increase the value of M or the value of the volatile suspended solids in the system by increasing the sludge recycle rate relative to influent rate, decreasing sludge purge from the system or a combination of both.
- It will be understood that while each of these individual techniques can be used separately to alter F/M ratios and BOD/P ratios, it is also possible to use various techniques in combination. Thus, for example, increasing influent flow rate while decreasing sludge recycle rate will have a more significant effect on increasing the F/M ratio but will not necessarily alter the BOD/P ratio. As mentioned above, the further employment of the technique of adding BOD to the system will not only further increase the F/M ratio, but will also increase the BOD/P ratio.
- When operating in accordance with the improved procedure described above wherein the F/M and BOD/P ratios are controlled within certain ranges and relative to each other, it is also desirable to control the Influent Detention Time (IDT) of the anaerobic, oxic, and anoxic treatments. Particularly, it is desirable to control the IDT's of the anaerobic and oxic treatments relative to each other.
- Generally, it is desirable to control the IDT of the anaerobic treatment such that it represents at least 5% of the total IDT of the entire process system. Usually, the IDT of the anaerobic treatment represents at least 10% or even 20% of the total IDT of the process system. On the other hand, the IDT of the anaerobic treatment is usually controlled such that it constitutes no more than 80% of the total IDT of the process system. Typically, the IDT of the anaerobic treatment is no more than 70% or even 60% of the total IDT of the process system.
- The IDT of the oxic treatment for typical operations is controlled so that it comprises at least 20% of the total IDT of the process system. Controlling the oxic IDT so as to constitute at least 30% or even 40% of the total IDT of the process system is quite satisfactory. Normally, the IDT of the oxic treatment is controlled such that it represents less than 95% of the total IDT of the process system and, generally, is controlled so as to constitute less than 90% or even less than 80% of the total IDT of the process system.
- When operating with a system wherein the influent also contains ammonia values and such components are subjected to nitrification and denitrification under anoxic conditions, the IDT of the anoxic treatment is controlled so as to comprise at least 5% and usually at least 10% of the total IDT of the process system. Conversely, the IDT of the anoxic treatment is controlled so that it comprises no more than 50% of the total IDT of the process system. Typically, the IDT of the anoxic treatment is controlled so that it constitutes less than 30% or even less than 20% of the total IDT of the process system.
- Another way of expressing the limits regarding the control of IDT's during the anaerobic and oxic treatments is to maintain control of the anaerobic and oxic treatment IDT's based upon the total IDT for only the anaerobic and oxic treatments, even if there are additional treatments in the process, such as, for example anoxic treatment. When expressed in this manner, the IDT of the anaerobic treatment is to be at least 10% of the combined anaerobic and oxic IDT's while the IDT of the anaerobic zone should be controlled so as to be no greater than 70% or even 60% of the combined anaerobic and oxic IDT's. Conversely, the IDT in the oxic treatment is to be controlled such that it comprises no more than 90% of the combined anaerobic and oxic lOTs. On the other hand, the IDT of the oxic treatment is to be controlled so as to comprise at least 30% or even 40% of the combined anaerobic and oxic lOTs.
- This invention also allows of the conduct of biological processes, such as, for example, fermentation, including the production of biosynthetic medicaments, in a controlled manner so as to obtain rapid incorporation of phosphorous into the active biomass. The result of this is, of course, the maintenance of a biological population of high phosphorous content providing the advantages of ready separation of the more dense biomass from the liquor containing the product. Further, the resulting high phosphorous content biomass contains its own internal source of energy, which permits the valuable biomass to survive anerobic conditions or to stand up to oxygen deficiencies in the system.
- In the attached drawing the Figures are schematic representations of two differing "type" processes in which the present invention can be utilized.
- Figure 1 represents a simplified diagram illustrating the basic type process to which this invention relates.
- Figure 2 is a diagramatic representation of another type system in which nitrification and denitrification are practiced.
- Figure 3 is a simplified diagram illustrating an alternative flow scheme for a nitrification-denitrification system.
- Figure 4 is a simplified plan view illustrating an installed plant embodying a process of the type described in the prior art and the corrective action which can be taken to gain the advantages of the present improvement.
- Referring now to Figure 1, an activated biomass system is illustrated having an inlet line 10 for the introduction of a BOD- and phosphorus-containing influent. Typically, the influent can be wastewater from a primary sedimentation tank in a sewage treatment operation. Alternatively, the influent could be a BOD- and phosphorus-containing charge stock to a fermentation process. The influent initially enters an
anaerobic mixing zone 12 wherein it is admixed with activated biomass introduced into mixingzone 12 by means of sludge recycleline 14 in order to form a mixed liquor. The anaerobic conditions defined above can be maintained, for example, by blanketing the liquid surface inzone 12 with nitrogen or other inert gas or by providing a cover to zone 12. Another means for insuring the maintenance of anaerobic conditions inzone 12 is to bubble nitrogen through the liquid in order to strip any oxygen therefrom. This particular technique is illustrated by means of manifoldnitrogen inlet line 16 shown in Figure 1 as introducing nitrogen into the bottom ofzone 12. - The mixed liquor formed in
anaerobic mixing zone 12 is then passed by means ofline 18 into oxic treatingzone 20 wherein the mixed liquor is contracted with an oxygen-containing gas. In Figure 1 this is illustrated by means ofspargers 22 designed to permit the contacting of mixed liquor with an oxygen-containing gas such as air, oxygen, or oxygen enriched air. - Subsequent to the oxic treatment, the mixed liquor from oxic treating
zone 20 is passed by means ofline 24 intoclarifier 26 wherein the mixed liquor is permitted to separate into a supernatant liquid phase and a more dense activated biomass phase. The supernatant liquid is removed fromclarifier 26 by means ofline 28 and then can be sterilized via ozone, chlorine or chlorine dioxide contacting and discharged to receiving waters, when the process is an activated sludge sewage treatment process. Alternatively, when the treatment is, for example, a fermentation process, the liquid ofline 28 can be recovered as the product-containing stream. - The dense activated
biomass layer 29 is maintained at a desired level by controlled removal fromclarifier 26 by means ofline 30. A portion of this activated biomass is removed from the system byline 32, while another portion of the activated biomass is recycled to theanaerobic mixing zone 12 by means ofpump 33 andline 14. - While
anaerobic mixing zone 12 can be a single treating stage, it is preferred to divide the anaerobic zone into a plurality of separate hydraulic stages. As illustrated in Figure 1, this can be accomplished through the use of partitions 34 which divideanaerobic zoning 12 into three interconnected stages. It will also be understood, of course, thatzone 12 can be divided into a greater or lesser number of stages. - Similarly, it is also preferred to have the oxic treating
zone 20 divided into a plurality of interconnected hydraulic stages. This is illustrated in Figure 1 by means of the twopartitions 36 which dividezone 20 into three stages. Again, it will be understood thatzone 20 can also be divided into a greater or lesser number of stages. - In practice, a process of the type illustrated by Figure 1 operates to effect incorporation of large quantities of phosphorus into the activate biomass, while causing the elimination of BOD from the liquid portion of the material treated; thereby providing a liquid effluent in
line 28 of substantially reduced BOD and P content while providing an activated biomass, such as that removed from the clarifier by means ofline 30, having a relatively high phosphorus content. The process system shown in Figure 1 to which the parameters of this invention relate is that portion of the flow scheme of Figure 1 enclosed within the dashed lines. - Referring now to Figure 2, an activated biomass system having nitrification and denitrification capabilities is illustrated. This system has an
inlet line 40 for the introduction of a BOD-, phosphorus-, and ammonia-containing influent. The influent is most typically a municipal or industrial wastewater stream. Alternatively, the influent can be the charge stock to a biosynthetic process, e.g. fermentation. The influent ofline 40 initially enters ananaerobic mixing zone 42 wherein it is admixed with activated biomass introduced into mixingzone 42 by means of sludge recyclepump 69 andline 44 in order to form a mixed liquor. - The mixed liquor formed in
anaerobic mixing zone 42 is then passed by means ofline 46 intoanoxic treating zone 48 wherein the mixed liquor, containing BOD, is treated in the substantial absence of dissolved oxygen in order to convert nitrites and/or nitrates (NOX) into gaseous form, primarily N2, which is then removed from the system by bubbling off. - The techniques for insuring the absence of dissolved oxygen in both
anaerobic mixing zone 42 andanoxic treating zone 48 can be the same as those discussed above in connection with the description of Figure 1. Again, as in Figure 1, the technique illustrated is the bubbling of nitrogen through the mixed liquor in order to strip oxygen therefrom. This particular technique is illustrated by means of manifoldednitrogen inlet line 50 shown in Figure 2 as introducing nitrogen into the bottoms of bothzone 42 andzone 48. - Subsequent to the anoxic treatment in
zone 48, the mixed liquor therefrom isd passed by means ofline 52 into oxic treatingzone 54. The mixed liquor introduced into oxic treatingzone 54 still contains P, BOD, ammonia and ammoniacal compounds, which latte two materials pass throughanaerobic mixing zone 42 andanoxic treating zone 48 substantially unaffected. In oxic treatingzone 54 this mixed liquor is contacted with an oxygen-containing gas. In Figure 2 this is illustrated by means ofspargers 56 designed to permit the contacting of mixed liquor with an oxygen-containing gas such as air, oxygen, or oxygen enriched air. Among other thins, this treating of the mixed liquor with oxygen is effective to convert ammonia and ammoniacal compounds into nitrites and/or nitrates. A portion of the mixed liquor containing these nitrites and nitrates is internally recycled from oxic treatingzone 54 to anoxic treatingzone 48 by means ofpump 57 andinternal recycle line 58. The material internally recycled by means ofpump 57 andline 58 is the source of NOX subjected to the anoxic treatment inzone 48 as described previously. - Subsequent to the oxic treatment in
zone 54, the mixed liquor therefrom is passed by means ofline 60 intoclarifier 62 wherein the mixed liquor is permitted to separate into a supernatant liquid phase and a moredense layer 65 of activated biomass. The supernatant liquid is removed fromclarifier 62 by means ofhne 64. This liquid can, if required, be sterilized and discharged to a stream or river in the form of purified water, when the process is an activated sludge sewage treatment process. - The more
dense layer 65 of activated biomass is maintained at a desired level by controlled removal fromclarifier 62 by means ofline 66. A portion of this activated biomass is removed from the system byline 68, while another portion of the activated biomass is recycled to theanaerobic mixing zone 42 by means of sludge recyclepump 69 andline 44. - While the
anaerobic mixing zone 42, theanoxic treating zone 48 and the oxic treatingzone 54 can each be a single treating stage, it is preferred to divide each of these stages into a plurality of interconnected hydraulic stages. As illustrated in Figure 2 this can be accomplished through the use of partitions and two each ofpartitions 70, 72 and 74 are shown dividinganaerobic mixing zone 42,anoxic treating zone 48 and oxic treatingzone 54, respectively, each into three separate stages. It will be understood, of course, that each of the zones can be divided into a greater or lesser number of individual stages and that it is not necessary for each of the zones to be divided into the same number of stages. - The process system shown in Figure 2 to which the parameters of this invention relate is that portion of the flow scheme enclosed within the dashed lines.
- Referring now to Figure 3, there can be seen a diagram of an activated biomass system having nitrification-dinitrification capabilities and having a flow scheme which is an alternative to that illustrated in Figure 2. This system has an
inlet line 80 for the introduction of a BOD-, phosphorous-, and ammonia-containing influent into ananaerobic mixing zone 82 wherein it is admixed with activated biomass introduced into mixingzone 82 by means of sludge recycleline 84 in order to form a mixed liquor. - The mixed liquor formed in
anaerobic mixing zone 82 is then passed by means ofline 86 into oxic treatingzone 88. The mixed liquor introduced intozone 88 still contains BOD as well as P, ammonia and ammoniacal compounds, which latter two materials pass throughanaerobic mixing zone 82 substantially unaffected. In oxic treatingzone 88, this mixed liquor is contacted with an oxygen-containing gas. As in the preceding figures, this is illustrated by means of spargers 90 designed to permit the contacting of mixed liquor with an oxygen-containing gas such as air, oxygen or oxygen- enriched air in order to effect P and BOD removal. The previously unaffected ammonia and ammoniacal compounds in the mixed liquor are converted also into nitrites and/or nitrates (NOX) and this NOX containing mixed liquor is then passed from an oxic treatingzone 88 by means ofline 92 and introduced intoanoxic treating zone 94 wherein NOX is reduced largely to elemental nitrogen by oxygen demand of the biomass in the mixed liquor. In the event that additional BOD is required for more complete denitrification, BOD from external sources can be added to anoxic treatingzone 94 by means ofsupplemental food line 81, influent by-pass line 83 or a combination of both. - While various techniques can be employed to insure the low dissolved oxygen content required for anaerobic and anoxic conditions, the technique illustrated in this figure is the employment of a manifolded
nitrogen inlet line 96 designed to introduce nitrogen into the bottoms ofzones - Mixed liquor is then removed from anoxic treating
zone 94 by means ofline 98 and this nitrified- denitrified and BOD reduced mixed liquor is introduced intoclarifier 100 wherein the mixed liquor is permitted to separate into a supernatant liquor phase and alayer 103 of more dense activated biomass. The supernatant liquid is removed fromclarifier 100 by means ofline 102 for disposition or further processing. The more dense activated biomass is maintained at a desired level by controlled removal fromclarifier 100 by means ofline 104. A portion of this activated biomass is removed from the system by means ofline 106, while another portion of the activated biomass is recycled to theanaerobic mixing zone 82 by means ofrecycle pump 107 andline 84. - Also shown in dotted lines in Figure 3 is an additional and optional
oxic treatment zone 110 having asparger 108. This optionaloxic treatment zone 110 is shown as being located between anoxic treatingzone 94 andclarifier 100. This optional treating zone can be employed if it is desired to increase the dissolved oxygen content of the mixed liquor before introducing it into theclarifier 100. - The portion of the system shown in Figure 3 to which the parameters of this invention relates is enclosed with a dashed line.
- In figure 4 there is shown a schematic plan view representing a hypothetical installed wastewater treating plant composed of two trains which are mirror images of each other.
- In this figure there is illustrated a wastewater influent line 112 which is split into
lines zones sludge inlet lines zones - Treating
zones - Subsequent to the anaerobic treatment in
zones anoxic treatment zones zones zones zones - Thereafter the mixed liquor from
zones zones oxygen inlet manifolds zones zones - Also shown in this figure are mixed liquor
internal recycle lines zones zones - The mixed liquor from oxic treating
zones anoxic treating zones - Finally the mixed liquor from second
anoxic zones oxic zones Oxygen inlet lines zones zones lines 156 and 158, respectively, to clarifier 160. This high DO level tends to keep the separated sludge from going anaerobic which would permit phosphorus bleed-out from the biomass. -
Clarifier 160 operates by permitting the separation of the mixed liquor into a more dense active biomass phase and a supernatent liquid phase, which liquid phase is removed fromclarifier 160 by means ofline 162. The more dense activated biomass is removed fromclarifier 160 by means ofline 164. A portion of the separated biomass is removed from the system by means ofline 166, while another portion of the activated biomass is recycled to the initial anaerobic treating zone by means ofline 168 which in turn connects withlines - A not untypical wastewater treating plant of the type described above and illustrated in figure 4 would have an IDT for all of the treating zones in the range of about 16 to 20 hours. Further the distribution of such total IDT, on a percentage basis, for the various treating zones illustrated would be about as follows:
- Anaerobic treatment (
zones 118, 120) - 8 to 10% - First anoxic treatment (
zones 128, 130) - from about 15 to about 20% - First oxic treatment (
zones 132, 134) - 35 to 45% - Second anoxic treatment (
zones 144, 146) - 25 to 30% - Final oxic treatment (
zones 148, 150) - 8 to 10%. - A system of this type having a protracted IDT would undoubtedly have a comparatively low F/M ratio relative to the particular BOD/P ratio existing in the influent. In accordance with the present improvement, the proposed method of controlling F/M and BOD/P ratios is simply to install
valves lines line 168 to a level of 50% of its former value while simultaneously closingvalves line 116 and into the initial anaerobic treatingzone 120 while diverting the now 50% reduced flow of recycle activated sludge fromline 168 throughline 124 and into anaerobic treatingzone 120. In effect, the entire parallel train composed ofzones line 156 is shut down and removed from the process system. Such procedures would leave unchanged the BOD/P ratio while substantially doubling the F/M ratio and result in a total IDT for the process system in the range from about 8 to 10 hours. - In order to illustrate this invention in greater detail, reference is made to the following examples in which wastewater from a variety of municipalities was tested.
- A series of experiments was conducted employing as influents samples of municipal wastewaters. In Examples 1 through 11, total BOD5 of the influents varied from about 30 to about 155 milligrams per liter (mg/I) with the soluble BODs of the influents varying from about 9 to about 40 mg/I. The phosphorous content of the influents also varied from about 1.5 to about 9 mg/I. In Examples 1 through 8, a process of the type illustrated in Figure 1 was employed, while in Examples 9 through 11 a nitrification-denitrification operation of the type illustrated in Figure 2 was employed. The recycling of mixed liquor from the oxic zone to the anoxic zone in the Figure 2 type operation is referred to as internal recycle. Various data and operating parameters for Examples 1 through 11 are set forth in the following Table I.
-
-
- Referring now to the data in Table I, Example 1 illustrates operation employing a BOD/P ratio outside the scope of this invention, i.e. less than about 5, even though the F/M ratio was well into the acceptable range. Although this particular operation did result in substantial reduction in the BOD content and phosphorous content of the influent, the value of k1 was less than 0.5.
- In Examples 2 through 11, the BOD/P ratio maintained was in the low range from about 5:1 up to about 10:1 and the F/M ratios varied within the defined limits. Examples 2 and 3, derived from different municipal wastewaters, illustrate that while the BOD/P ratios were within the limits required by the invention, the F/M ratios were just below the low end of the required envelope and the rate of removal of phosphorous was not consistently above the minimum level represented by a k,, value greater than 0.5.
- Examples 4 through 8 illustrate other experimental runs operating with similar BOD/P ratios but with increasing F/M ratios. Again, it is interesting to note that the highest value for k1 of these five examples was achieved in Example 5, the one with the shortest detention time. (This excludes the results of anomalous Example 3.)
- Examples 9 through 11 illustrate an operation of the type illustrated in Figure 2 where the ammonia content of the influent was subjected to nitrification in an oxic zone and denitrification in an anoxic zone. The internal recycle rates for these three examples approached 200%. It will be noted that in Example 9 the F/M ratio was outside the range defined by the present invention and the k1 value was substantially below the required 0.5 level. On the other hand, however, in Examples 10 and 11, wherein BOD/P and F/M ratios within the defined ranges were employed, the values for k, were relatively high.
- Another series of experiments was conducted employing as the influent to each experiment a sample of a municipal wastewater. In Examples 12 through 20, total BOD, of the several influents varied from about 40 to about 170 mg/I with the soluble BOD, varying from about 30 to about 100. The phosphorus content of the several influents also varied from about 1 to about 5.5 mg/I. In Examples 12 through 17, a process of the type illustrated in Figure 1 was employed, while in Examples 18 through 20, a nitrification-denitrification operation of the type illustrated in Figure 2 was employed. Various data and operating parameters for Examples 12 through 20 are set forth in the following Table II.
- Generally the data in Table II illustrates operations employing a BOD/P ratio in the range from about 10:1 up to about 20:1. Examples 12 and 13, employing different municipal wastewaters, illustrate that while the BOD/P ratios were within the limits required by the invention, the F/M ratios were just below the low end of the required envelope and the rate of removal of phosphorous was not consistently above the minimum level represented by a k1, value greater than 0.5. Examples 14 through 17 illustrate other experimental runs operating with similar BOD/P ratios but with increasing F/M ratios. Again, it will be seen that in many instances the result of decreasing detention time is to increase the value of the ki factor.
- Examples 18 through 20 exemplify an operation of the type illustrated in Figure 2 where the ammonia in the influent was subjected to nitrification in an oxic zone and denitrification in an anoxic zone. The internal recycle rates for these three examples varied from about 100 to about 200 per cent. In Example 18 it will be seen that the value of the F/M ratio fell below the minimum acceptable level of 0.09 and that the value of k, also fell below the minimum standard of 0.5. When operating with the scope of this invention, as illustrated by Examples 19 and 20, the k, factor was substantially greater and above the minimum acceptable level.
- A further series of experiments was conducted employing a variety of BOD- and phosphorus containing influents. In these examples the total BOD, varied from about 140 to about 380 mg/I with the soluble BOD, varying from about 85 to about 155 mg/I. The phosphorus content of the influents also varied from about 4 to about 7 mg/I. In Examples 21 through 24 a process of the type illustrated in Figure 1 was employed, while in Example 25 a nitrification-denitrification operation of the type illustrated in Figure 2 was employed. The data and operating parameters for Examples 21 through 25 are set forth in Table III below.
- It will be seen that the examples shown in Table III operated at a BOD/P ratio in the broad range of about 20:1 up to about 50:1, but generally at a level of less than about 30:1.
- Review of this data in Table III indicates the operability of the improvement of this invention when operating within the BOD/P and F/M ratios required by the invention in order to provide a k, factor having a value greater than 0.5.
Claims (23)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT80106093T ATE4045T1 (en) | 1979-10-09 | 1980-10-07 | CONTROL OF ACTIVATED SLUDGE PROCESS TO ACHIEVE HIGHER PHOSPHORUS REMOVAL RATES. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US83196 | 1979-10-09 | ||
US06/083,196 US4271026A (en) | 1979-10-09 | 1979-10-09 | Control of activated sludge wastewater treating process for enhanced phosphorous removal |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0026938A1 EP0026938A1 (en) | 1981-04-15 |
EP0026938B1 true EP0026938B1 (en) | 1983-07-06 |
Family
ID=22176790
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19800106093 Expired EP0026938B1 (en) | 1979-10-09 | 1980-10-07 | Control of activated sludge wastewater treating process for enhanced phosphorus removal |
Country Status (13)
Country | Link |
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US (1) | US4271026A (en) |
EP (1) | EP0026938B1 (en) |
JP (1) | JPS57113893A (en) |
AT (1) | ATE4045T1 (en) |
AU (1) | AU531468B2 (en) |
CA (1) | CA1143486A (en) |
DE (1) | DE3064050D1 (en) |
DK (1) | DK421580A (en) |
ES (1) | ES495736A0 (en) |
FI (1) | FI803148L (en) |
GR (1) | GR70762B (en) |
IL (1) | IL61159A (en) |
ZA (1) | ZA806238B (en) |
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DK421580A (en) | 1981-04-10 |
EP0026938A1 (en) | 1981-04-15 |
ATE4045T1 (en) | 1983-07-15 |
IL61159A0 (en) | 1980-11-30 |
ZA806238B (en) | 1981-09-30 |
AU6304880A (en) | 1981-04-16 |
IL61159A (en) | 1983-07-31 |
US4271026A (en) | 1981-06-02 |
AU531468B2 (en) | 1983-08-25 |
GR70762B (en) | 1983-03-16 |
CA1143486A (en) | 1983-03-22 |
JPS6312680B2 (en) | 1988-03-22 |
ES8107131A1 (en) | 1981-09-16 |
DE3064050D1 (en) | 1983-08-11 |
ES495736A0 (en) | 1981-09-16 |
FI803148L (en) | 1981-04-10 |
JPS57113893A (en) | 1982-07-15 |
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